Mortality among 2,113 U.S. and Canadian members of the Pulp, Sulfite, and Paper Workers' Union, 1935 through 1964, was studied using a proportionate mortality analysis. Mortality due to gastric cancer was found to be elevated in all jurisdictions, but only in mills using sulfate or sulfite pulping. An excess of mortality due to kidney cancer was limited to mills in Oregon and Washington. Excesses of deaths due to leukemia, Hodgkin's disease, and lymphosarcoma were observed only in mills in Oregon, Washington, and Wisconsin and the province of Quebec. Based on small numbers, excesses of deaths due to cancers of rectum, pancreas, kidney, and lymphosarcoma were seen primarily among sulfite process workers, while Hodgkin's disease deaths occurred primarily in sulfate (kraft) process workers. These findings suggest that cancer mortality in pulp and paper workers may be related both to pulping process and to tree species processed.